Population Genetic Diversity Of Chinese Mitten Crab (Eriocheir Sinensis) In Odd And Even Years In The Yangtze And Liaohe Rivers

Chinese Mitten crab（Eriocheir sinensis）,commonly known as E.sinensis and hairy crab,is a famous freshwater species with Chinese characteristics and a foreign exchange earning aquatic product for export.E.sinensis are abundant and widely distributed,especially in the Yangtze River,Liaohe River and Oujiang River basin.Since 1980s,the breeding industry of E.sinensis has developed rapidly,and the crab seedling resources are in short supply.In order to solve the shortage problem,some breeding enterprises blindly introduced the parents and seedlings of E.sinensis from other places,lacking the awareness of germplasm protection,resulting in the risk of resource degradation and confounding of E.sinensis germplasm.In order to investigate the germplasm status of wild E.sinensis in the Yangtze River basin,we analyzed the genetic diversity and gene flow among different populations of E.sinensis in the Yangtze River（Anqing,Taizhou,Shanghai）and Liaohe River（Liaohe）in odd and even years based on D-loop sequence of mitochondrial DNA and microsatellite markers.At the same time,in order to reveal the potential morphological differences of different populations of E.sinensis,the geometric morphological characteristics of different populations of E.sinensis were analyzed.The results are as follows:1.Results of geometric morphometry analysis:In the morphological analysis of wild E.sinensis in odd-year,the highest contribution rate was the first tooth,which was higher than 60%.The discriminant analysis based on Bayes method showed that the Liaohe population and the Yangtze River population could be clearly distinguished,and the discriminant accuracy of each population was 94.2%-100%in the step by step discriminant analysis,which had a high accuracy.In the morphological analysis of wild E.sinensis in even-year,the highest contribution rate was still the first tooth,which was higher than 40%.It was found that the Liaohe population and the Yangtze River population could be clearly distinguished from each other in the mottled analysis.In the stepwise discriminant analysis,the discriminant accuracy of each population was 90.8%to 95.2%,which was relatively high,but there was a certain probability of misjudgment.2.Results of sequence genetic analysis based on D-loop region:The odd-year populations in both drainage basins had high haplotype diversity（0.714-0.952）and high nucleotide diversity（0.004-0.174）.A total of 17 haplotypes were identified,of which 3 shared haplotypes.The gene flow between Liaohe River population and Taizhou population was greater than 1（1.903）,indicating that there was strong gene flow between the two basin populations and a close genetic relationship.Genetic differentiation coefficient(F_ST)showed that there was a certain degree of genetic differentiation in the four populations(F_ST=0.243).The results of paired F_STshowed that there was high genetic differentiation between Liaohe population and Yangtze River population(F_ST=0.208-0.406),while low genetic differentiation between Yangtze River population and Yangtze River population(F_ST=-0.020-0.080).The 4 populations in even years had high haplotype diversity（0.905-1.000）and high nucleotide diversity（0.009-0.016）,and 22 haplotypes were identified,two of which shared haplotypes,showing rich genetic diversity.There was moderate genetic differentiation between Liaohe population and Yangtze River basin population(F_ST=0.050-0.229),and there was also genetic differentiation between Yangtze River population(F_ST=0.098).There was moderate genetic differentiation between odd and even-year populations in Liaohe population(F_ST=0.186).There was strong gene flow in odd and even-year populations in the Yangtze and Liaohe river basins（Yangtze River N_m=10.614;N_m=2.185）haplotype network map of Liaohe River basin showed that there were more missing haplotypes between the odd and even years haplotypes of the Yangtze River basin and the Liaohe River basin population,with local radiative structure and some genetic differences.3.Genetic analysis results based on microsatellite markers:The overall degree of genetic differentiation of odd-year populations with different water basins was low(F_ST=0.019),but the paired F_ST results showed that there was genetic differentiation among the four populations(F_ST=0.009-0.097),and there was genetic differentiation between the Liaohe River population and the Yangtze River population(F_ST=0.088-0.097).The degree of genetic differentiation among Yangtze River populations was low(F_ST=0.009-0.026).The results of principal coordinate analysis show that the Yangtze River population is obviously clustered into a branch,which is far away from the Liaohe population,which is the same as the D-loop analysis results.Although geographically far apart,there was strong gene flow（N_m=6.524-7.750）between the two river populations.The overall degree of genetic differentiation of E.sinensis population in even years of two river basins was low(F_ST=0.025),the coefficient of genetic differentiation between Liaohe and Shanghai populations was 0.107,and the coefficient of genetic differentiation between Yangtze River populations was 0.010-0.120.STRUCTURE analysis could not effectively distinguish the Yangtze River population from the Liaohe population,indicating that the genetic background of the four populations is similar.There was significant genetic differentiation among odd-year and even-year populations in the whole population(F_ST=0.108),moderate genetic differentiation between odd-year and even-year populations in Liaohe population(F_ST=0.130),and moderate genetic differentiation between odd-year and even-year populations in the Yangtze River(F_ST=0.134).There was strong gene flow in odd and even year populations in the Yangtze River and the Liao River（Yangtze River N_m=1.611;Liaohe N_m=1.671）;The results of STRUCTURE analysis showed that the population of odd years and even years belonged to two different genetic clusters.In conclusion,in this study,geometric morphometry was used to distinguish wild E.sinensis from different basins with high accuracy.The genetic diversity of wild E.sinensis in the Yangtze River and Liaohe River is relatively rich,and it is still a relatively high quality germplasm resource.The existence of moderate to strong gene flow between the populations of the two basins suggests the urgent need to strengthen the protection of wild resources and avoid genetic homogeneity.The wild E.sinensis（odd-year and odd-year）in the two basins can be distinguished as two distinct genetic lineages,but there is gene exchange between odd-year and odd-year genetic lineages.This study elucidates the genetic resources of wild E.sinensis and lays a foundation for the conservation and development of germplasm resources.